The proposed research will examine the neural loci mediating the behavioral effects of androgens in male mammals. It will also study the role of metabolism versus structure in androgen action on the brain. The research will be done using two types of comparative analysis. The neural loci and mechanism of androgen action will be compared across species for certain behaviors (e.g. comparisons of sexual behavior in rats and gerbils, or comparisons of scent marking in gerbils and mice) and across behavior patterns within species (e.g. comparisons of sexual behavior and sent marking in gerbils or comparisons of sent marking and ultrasound production in mice). Studies concerning the neural loci involved in androgen-dependent behaviors will be done using hormone implants directly into the brain and using lesion techniques. Studies of the role of androgen metabolism will be done by assessing the amounts of radiolabeled steroids in the nuclei of hypothalamic cells from males treated with various hormones or with hormone-drug combinations.